The problem with these error messages is that I never exactly know where the problem is. I noticed that the method I was using didn't really exist (even reference documentation on glsl is bizarrely wanting) and replaced it now with texture2D. The following is the fragment shader, now. Would you like to have a look at the vertex shader, just in case?

It works, I was being stupid. But it's not perfect yet. Even though the first line of the vertex shader is attribute vec4 tangent, jpct tells me

Quote

Tangent handle not found (tangents needed: true)!

Also, it's in the wrong place, and I suspect it's because I didn't fill a uniform vec4 vViewPosition variable. The following is the short vertexshader code. Please help me find how to fill vViewPosition (I don't suppose it's just the cameraPosition because of that pesky fourth value). Is it, perhaps, a 2x2 Matrix?